On-demand snapshot and prune in a data storage system

ABSTRACT

A method of data progression in a data storage system having at least two tiers of storage space. A first tier may include storage space in a SLC SSD and a second tier may include storage space in a MLC SSD. The method may include setting a predetermined free space threshold for the first tier of storage space, monitoring free space in the first tier of storage space, and when the amount of available free space in the first tier of storage space decreases to the predetermined free space threshold, generating an on-demand snapshot of at least a portion of the data of the first tier of storage space by designating that data as read-only. The on-demand snapshot may then be transferred to the second tier of storage space, thereby freeing the corresponding portion of data of the first tier of storage space for new writes.

FIELD OF THE INVENTION

The present disclosure relates generally to data progression in a datastorage system. Particularly, the present disclosure relates togenerating snapshots, as at least a part of overall data progression, inan unconventional on-demand manner. More particularly, the presentdisclosure relates to data progression in a data storage system havingsingle level cell (SLC) and multilevel cell (MLC) solid state devices orother hybrid or tiered-based storage, wherein snapshots are generated inan unconventional on-demand manner to move or progress data from SLC toMLC devices, or generally from one tier of storage to another lower costtier, when more desirable.

BACKGROUND OF THE INVENTION

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

As the value and use of information continues to increase, individualsand businesses seek additional ways to process and store information.One option available to users is information handling systems. Aninformation handling system generally processes, compiles, stores,and/or communicates information or data for business, personal, or otherpurposes thereby allowing users to take advantage of the value of theinformation. Because technology and information handling needs andrequirements vary between different users or applications, informationhandling systems may also vary regarding what information is handled,how the information is handled, how much information is processed,stored, or communicated, and how quickly and efficiently the informationmay be processed, stored, or communicated. The variations in informationhandling systems allow for information handling systems to be general orconfigured for a specific user or specific use such as financialtransaction processing, airline reservations, enterprise data storage,or global communications. In addition, information handling systems mayinclude a variety of hardware and software components that may beconfigured to process, store, and communicate information and mayinclude one or more computer systems, data storage systems, andnetworking systems.

Some information handling systems, such as storage centers or other datastorage systems or subsystems, comprising mass storage devices, such asbut not limited to disk drives, solid state drives, or virtual diskdrives allow the efficient storage of data by allocating user dataacross a pool of storage and a plurality of drives based on, forexample, RAID-to-disk mapping. Data progression may be utilized in suchsystems to move data gradually to storage space of appropriate overallcost for the data, depending on, for example but not limited to, thedata type or access patterns for the data. In addition, such drivesystems may protect data from, for example, system failures or virusattacks by automatically generating and storing snapshots orpoint-in-time copies (PITCs) of the system or matrix of drive storageblocks at, for example, predetermined time intervals, user configureddynamic time stamps, such as, every few minutes or hours, etc., or attimes directed by the server. These time-stamped snapshots permit therecovery of data from a previous point in time prior to the systemfailure, thereby restoring the system as it existed at that time. Suchsystems are further described in U.S. Pat. No. 7,613,945, titled“Virtual Disk Drive System and Method,” issued Nov. 3, 2009, U.S. Pat.No. 8,468,292, titled “Solid State Drive Data Storage System andMethod,” issued Jun. 18, 2013, and U.S. patent application Ser. No.13/429,511, titled “Single-Level Cell and Multi-Level Cell Hybrid SolidState Drive,” filed Mar. 26, 2012, each of which is incorporated byreference herein in its entirety.

One problem that may exist in such systems, however, is that in certaincircumstances, a snapshot or PITC may unnecessarily consume space in ahigher cost storage tier. For example, PITCs in any given system may beconfigured to expire after a certain amount of time or based on theoccurrence of a specific event or number of events, etc. In many cases,after a PITC expires, it no longer needs to be stored in the system nordoes it need to be available for users. However, if such an expired PITChas the active PITC (i.e., the current volume or PITC that handles writerequests) as its child and coalescing with the active PITC is notpermitted or is otherwise disabled, then the expired PITC will often bein a frozen state until another snapshot is taken before coalescing ofthe expired PITC is possible, thereby holding allocated pages of datahostage in a higher cost storage tier, resulting in unnecessary spaceconsumption of the higher cost storage, which is often more desirablyutilized for active data pages. FIG. 1, which shows an active PITC 102and its parent PITC 104, illustrates the unnecessary resulting spaceconsumption. In FIG. 1, a total of nine (9) data pages 106 are allocatedbetween the active PITC 102 and the frozen PITC 104. That is, nine pagesof data are currently allocated and unavailable for new writes. However,pages 1, 2, and 5 of the frozen PITC 104 have been “overwritten,” likelyutilizing a copy-on-write algorithm, as pages 6, 7, and 9 in the activePITC, and as such, pages 1, 2, and 5 simply become historical data,which desirably may be stored in lower cost storage for historicalpurposes, such as but not limited to, backup purposes. Yet, because PITC104 has the active PITC as its child and cannot be coalesced therewith,pages 1, 2, and 5 remain on high cost storage until another snapshot isgenerated, which depending on the system configuration or set-up, couldbe a significant span of time. Until another snapshot is generated,pages 1, 2, and 5 remain hostage, and cannot be reclaimed for better useof the space. Active PITCs, expiring PITCs, and coalescing PITCs aredescribed in further detail in U.S. Pat. No. 7,613,945, previouslyincorporated by reference herein.

For additional cost, solid state device systems, either comprising orconsisting entirely of solid state storage devices, such as SLC solidstate drives (SSDs) and/or MLC SSDs, can provide better input/output(I/O) performance as compared to storage systems consisting of only diskdrives. The read performance of SLC and MLC drives is essentially thesame. However, SLC drives typically have faster write performance andcan handle more write I/Os (i.e., have higher endurance or life span) ascompared to MLC drives. Accordingly, SLC drives are typically moreexpensive than MLC drives. To balance cost, life span, and performanceof a solid state device system, the system may be designed to have bothSLC and MLC drives, as described in detail in U.S. Pat. No. 8,468,292and U.S. patent application Ser. No. 13/429,511, which were previouslyincorporated by reference.

In such “hybrid” systems, SLC drive space may be preferred for new pagewrite I/O (i.e., where the system allocates a new page(s)), but thesystem may move to MLC drive space when the SLC space becomes fullyoccupied. If the hybrid system utilizes data progression or automatedtiering, then it could desirably move SLC pages that are part ofsnapshots or PITCs to lower cost tiers due to their lower usage, asdescribed in U.S. Pat. No. 8,468,292 and U.S. patent application Ser.No. 13/429,511. However, if the hybrid system does not utilize dataprogression or automated tiering, or if the system has volumes that aresnapshot capable but the system cannot or is not configured to takesnapshots at regular or otherwise predetermined intervals to move pagesto lower cost tiers, then such volumes will quickly and unnecessarilyconsume the SLC drive space as they continue to receive new page writeI/Os. Thus, the system will be more quickly required to rely on MLCdrive space for new page write I/Os. As this persists, it can reduceoverall write performance of the system and more quickly wear out theMLC drives.

In some solid state device systems, data progression or automatedtiering may usually move snapshot or PITC pages, due to their lowerusage, to MLC drives or other lower cost tier(s) (e.g., disk drives,which may also be tiered), which can help free up SLC drive space. Insuch systems, however, if coalescing snapshot or frozen PITCs into anactive PITC is enabled, then during coalesce, lower tier pages (ifpresent) in a frozen PITC will be moved to the active PITC. As a result,any writes to those lower tier pages of the active PITC will likely beslower and degrade overall system performance. Additionally, frequentwrites to the lower tier pages, if stored on MLC drive space, will morequickly wear out the MLC drive(s). If, on the other hand, the system isconfigured to move all lower tier pages of the active PITC (after acoalesce, for example) to a higher cost tier (such as a SLC tier) inorder to improve performance, then this will increase space consumptionin the higher cost tier, which could result with lower tier space beingutilized for new page I/O, which could also reduce overall systemperformance. For example, the active PITC may not receive write requestsfor some or many of the pages moved from the lower cost tier to thehigher cost tier, and thus the move would unnecessarily tie up highertier drive space.

Thus, there is a need in the art for improved data progression in a datastorage system. Particularly, there is a need in the art for methods andsystems for generating snapshots, as at least a part of overall dataprogression, in an on-demand manner. More particularly, there is a needin the art for methods and systems for data progression in a datastorage system having SLC and MLC devices or other hybrid ortiered-based storage, wherein snapshots are generated in anunconventional on-demand manner to move or progress data from SLC to MLCdevices, or generally from one tier of storage to another lower costtier, in a more desirable and efficient manner.

BRIEF SUMMARY OF THE INVENTION

The following presents a simplified summary of one or more embodimentsof the present disclosure in order to provide a basic understanding ofsuch embodiments. This summary is not an extensive overview of allcontemplated embodiments, and is intended to neither identify key orcritical elements of all embodiments, nor delineate the scope of any orall embodiments.

The present disclosure, in one embodiment, relates to a method of dataprogression in a data storage system having at least two tiers ofstorage space. A first tier may include storage space in a SLC SSD and asecond tier may include storage space in a MLC SSD. The method mayinclude setting a predetermined free space threshold for the first tierof storage space that is a threshold relating to the amount of freespace available on the first tier of storage space, monitoring freespace in the first tier of storage space, and when the amount ofavailable free space in the first tier of storage space decreases to thepredetermined free space threshold, generating an on-demand snapshot ofat least a portion of the data of the first tier of storage space bydesignating that data as read-only. The on-demand snapshot may then betransferred to the second tier of storage space, thereby freeing thecorresponding portion of data of the first tier of storage space for newwrites. The method may also include, in addition to generating on-demandsnapshots, generating snapshots of at least a portion of the data of thefirst tier of storage space and transferring at least some of thegenerated snapshots to the second tier of storage space at regularintervals. In some embodiments, the storage space of the SLC SSD may beconfigured as RAID 10 storage and the storage space of the MLC SSD maybe configured as RAID 5 storage. The data storage system may generallystore data for a plurality of logical volumes, and the on-demandsnapshot may be generated for data from one of the logical volumesutilizing the most storage space in the first tier. The data storagesystem may generally use copy-on-write techniques, and morespecifically, when a write operation is received by the data storagesystem directed to data stored by the on-demand snapshot, the writeoperation may be directed instead to newly allocated storage space ofthe first tier of storage space, and the corresponding data in theon-demand snapshot can be considered overwritten. The method may thusfurther include freeing overwritten data of the on-demand snapshot. Insome embodiments, the overwritten data of the on-demand snapshot may befreed substantially as soon as the data is overwritten. In otherembodiments, however, the overwritten data of the on-demand snapshot maybe freed according to a batch pruning method that operates on at least aportion of the second tier of storage space as a batch and frees alloverwritten data of the batch. The batch pruning method may be triggeredbased on a variety of events. However, in one embodiment, the batchpruning method may be triggered when the amount of available free spacein the second tier of storage space decreases to a predetermined freespace threshold for the second tier of storage. In another embodiment,the batch pruning method may be triggered according to a periodicschedule. In some embodiments, the on-demand snapshot may be generallyutilized internally solely by the data storage system and may notgenerally be accessible by a user of the data storage system.

The present disclosure, in another embodiment, relates to an informationhandling system including a data storage subsystem having at least twotiers of storage space, a first tier comprising storage space in asingle level cell (SLC) solid state device (SSD) and a second tiercomprising storage space in a multi-level cell (MLC) SSD. A controllermanaging the data storage subsystem may be configured to monitor freespace in the first tier of storage space, and when the amount ofavailable free space in the first tier of storage space decreases to apredetermined free space threshold, generate an on-demand snapshot of atleast a portion of the data of the first tier of storage space bydesignating that data as read-only. The controller may be furtherconfigured to transfer the on-demand snapshot to the second tier ofstorage space, thereby freeing the corresponding at least a portion ofdata of the first tier of storage space for new writes. As describedabove, in one embodiment, the storage space of the SLC SSD may beconfigured as RAID 10 storage and the storage space of the MLC SSD maybe configured as RAID 5 storage. A write operation received by the datastorage system directed to data stored by the on-demand snapshot maybedirected instead to newly allocated storage space of the first tier ofstorage space, and the corresponding data in the on-demand snapshot isconsidered to be overwritten. The controller may also be configured tofree overwritten data of the on-demand snapshot. As described above, thecontroller may be configured to free overwritten data of the on-demandsnapshot according to a batch pruning method that operates on at least aportion of the second tier of storage space as a batch and frees alloverwritten data. The batch pruning method may be run according to aperiodic schedule. As also generally indicated above, the on-demandsnapshot may be utilized internally by the controller and may notgenerally be accessible by a user of the data storage system.

While multiple embodiments are disclosed, still other embodiments of thepresent disclosure will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, thevarious embodiments of the present disclosure are capable ofmodifications in various obvious aspects, all without departing from thespirit and scope of the present disclosure. Accordingly, the drawingsand detailed description are to be regarded as illustrative in natureand not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter that is regarded as formingthe various embodiments of the present disclosure, it is believed thatthe invention will be better understood from the following descriptiontaken in conjunction with the accompanying Figures, in which:

FIG. 1 is a schematic representation of an active PITC and its parentPITC, illustrating an occurrence of unnecessary space consumption.

FIG. 2 is a schematic of an information handling system, in the form ofa data storage system, suitable for the various embodiments of on-demandsnapshot of the present disclosure.

FIG. 3 is a flow diagram of a method for on-demand snapshot prune inaccordance with an embodiment of the present disclosure.

FIG. 4A is a schematic representation of an on-demand snapshot or PITCand a child PITC before and after on-demand snapshot prune has beenperformed in accordance with an embodiment of the present disclosure.

FIG. 4B is a schematic representation of a frozen and expired PITCconverted into an on-demand snapshot or PITC in accordance with anembodiment of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to novel and advantageoussystems and methods for data progression in a data storage system.Particularly, the present disclosure relates to generating snapshots, asat least a part of overall data progression, in an unconventionalon-demand manner. More particularly, the present disclosure relates tosystems and methods for data progression in a data storage system havingSLC and MLC SSDs or other hybrid or tiered-based storage, whereinsnapshots are generated in an unconventional on-demand manner to move orprogress data from SLC to MLC devices, or generally from one tier ofstorage to another lower cost tier, in a more desirable and efficientmanner.

For purposes of this disclosure, any system or information handlingsystem described herein may include any instrumentality or aggregate ofinstrumentalities operable to compute, calculate, determine, classify,process, transmit, receive, retrieve, originate, switch, store, display,communicate, manifest, detect, record, reproduce, handle, or utilize anyform of information, intelligence, or data for business, scientific,control, or other purposes. For example, a system or any portion thereofmay be a personal computer (e.g., desktop or laptop), tablet computer,mobile device (e.g., personal digital assistant (PDA) or smart phone),server (e.g., blade server or rack server), a network storage device, orany other suitable device or combination of devices and may vary insize, shape, performance, functionality, and price. A system may includerandom access memory (RAM), one or more processing resources such as acentral processing unit (CPU) or hardware or software control logic,ROM, and/or other types of nonvolatile memory. Additional components ofa system may include one or more disk drives or one or more mass storagedevices, one or more network ports for communicating with externaldevices as well as various input and output (I/O) devices, such as akeyboard, a mouse, touchscreen and/or a video display. Mass storagedevices may include, but are not limited to, a hard disk drive, floppydisk drive, CD-ROM drive, smart drive, flash drive, or other types ofnon-volatile data storage, a plurality of storage devices, or anycombination of storage devices. A system may include what is referred toas a user interface, which may generally include a display, mouse orother cursor control device, keyboard, button, touchpad, touch screen,microphone, camera, video recorder, speaker, LED, light, joystick,switch, buzzer, bell, and/or other user input/output device forcommunicating with one or more users or for entering information intothe system. Output devices may include any type of device for presentinginformation to a user, including but not limited to, a computer monitor,flat-screen display, or other visual display, a printer, and/or speakersor any other device for providing information in audio form, such as atelephone, a plurality of output devices, or any combination of outputdevices. A system may also include one or more buses operable totransmit communications between the various hardware components.

While the various embodiments are not limited to any particular type ofinformation handling system, the systems and methods of the presentdisclosure may be particularly useful in the context of a storage centercomprising mass storage devices, such as but not limited to disk driveand solid state drive systems, or virtual disk drive systems, such asthat described in U.S. Pat. No. 7,613,945, U.S. Pat. No. 8,468,292, andU.S. patent application Ser. No. 13/429,511, which were previouslyincorporated herein by reference. Such data storage systems allow theefficient storage of data by dynamically allocating user data across apage pool of storage, or a matrix of drive storage blocks, and aplurality of drives based on, for example, RAID-to-disk mapping. Ingeneral, dynamic allocation presents a virtual disk or storage device orvolume to user servers. To the server, the volume acts the same asconventional storage, such as a disk drive, yet provides a storageabstraction of multiple storage devices, such as RAID (redundant arrayof independent disks) devices, to create a dynamically sizeable storagedevice. Data progression may be utilized in such disk drive systems tomove data gradually to storage space of appropriate overall cost for thedata, depending on, for example but not limited to, the data type oraccess patterns for the data. In general, data progression may determinethe cost of storage in the drive system considering, for example, themonetary cost of the physical storage devices, the efficiency of thephysical storage devices, and/or the RAID level of logical storagedevices. Based on these determinations, data progression may move dataaccordingly such that data is stored on the most appropriate coststorage available. In addition, such drive systems may protect datafrom, for example, system failures or virus attacks by automaticallygenerating and storing snapshots or point-in-time copies of the systemor matrix of drive storage blocks at, for example, predetermined timeintervals, user configured dynamic time stamps, such as, every fewminutes or hours, etc., or at times directed by the server. Thesetime-stamped snapshots permit the recovery of data from a previous pointin time prior to the system failure, thereby restoring the system as itexisted at that time. These snapshots or point-in-time copies may alsobe used by the system or system users for other purposes, such as butnot limited to, testing, while the main storage can remain operational.Generally, using snapshot capabilities, a user may view the state of astorage system as it existed in a prior point in time.

FIG. 2 illustrates one embodiment of a disk drive or data storage system200 in an information handling system environment 202, such as thatdisclosed in U.S. Pat. No. 7,613,945, U.S. Pat. No. 8,468,292, and U.S.patent application Ser. No. 13/429,511, and suitable with the variousembodiments of the present disclosure. As shown in FIG. 2, the diskdrive system 200 may include a data storage subsystem 204, which mayinclude, but is not limited to, a RAID subsystem, as will be appreciatedby those skilled in the art, and a disk or drive manager 206 having atleast one disk storage system controller. The data storage subsystem 204and disk/drive manager 206 can dynamically allocate data across drivespace of a plurality of disk drives or other suitable storage devices208, such as but not limited to optical drives, solid state drives, tapedrives, etc., based on, for example, RAID-to-disk mapping or otherstorage mapping technique. The data storage subsystem 204 may includedata storage devices distributed across one or more data sites at one ormore physical locations, which may be network connected. Any of the datasites may include original and/or replicated data (e.g., data replicatedfrom any of the other data sites) and data may be exchanged between thedata sites as desired.

In the various embodiments of the present disclosure, one or moreprograms or applications, such as a web browser, and/or otherapplications may be stored in one or more of the system data storagedevices. Programs or applications may be loaded in part or in whole intoa main memory or processor during execution by the processor. One ormore processors may execute applications or programs to run systems ormethods of the present disclosure, or portions thereof, stored asexecutable programs or program code in the memory, or received from theInternet or other network. Any commercial or freeware web browser orother application capable of retrieving content from a network anddisplaying pages or screens may be used. In some embodiments, acustomized application may be used to access, display, and updateinformation.

Hardware and software components of the present disclosure, as discussedherein, may be integral portions of a single computer or server or maybe connected parts of a computer network. The hardware and softwarecomponents may be located within a single location or, in otherembodiments, portions of the hardware and software components may bedivided among a plurality of locations and connected directly or througha global computer information network, such as the Internet.

As will be appreciated by one of skill in the art, the variousembodiments of the present disclosure may be embodied as a method(including, for example, a computer-implemented process, a businessprocess, and/or any other process), apparatus (including, for example, asystem, machine, device, computer program product, and/or the like), ora combination of the foregoing. Accordingly, embodiments of the presentdisclosure may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, middleware, microcode,hardware description languages, etc.), or an embodiment combiningsoftware and hardware aspects. Furthermore, embodiments of the presentdisclosure may take the form of a computer program product on acomputer-readable medium or computer-readable storage medium, havingcomputer-executable program code embodied in the medium, that defineprocesses or methods described herein. A processor or processors mayperform the necessary tasks defined by the computer-executable programcode. Computer-executable program code for carrying out operations ofembodiments of the present disclosure may be written in an objectoriented, scripted or unscripted programming language such as Java,Perl, PHP, Visual Basic, Smalltalk, C++, or the like. However, thecomputer program code for carrying out operations of embodiments of thepresent disclosure may also be written in conventional proceduralprogramming languages, such as the C programming language or similarprogramming languages. A code segment may represent a procedure, afunction, a subprogram, a program, a routine, a subroutine, a module, anobject, a software package, a class, or any combination of instructions,data structures, or program statements. A code segment may be coupled toanother code segment or a hardware circuit by passing and/or receivinginformation, data, arguments, parameters, or memory contents.Information, arguments, parameters, data, etc. may be passed, forwarded,or transmitted via any suitable means including memory sharing, messagepassing, token passing, network transmission, etc.

In the context of this document, a computer readable medium may be anymedium that can contain, store, communicate, or transport the programfor use by or in connection with the systems disclosed herein. Thecomputer-executable program code may be transmitted using anyappropriate medium, including but not limited to the Internet, opticalfiber cable, radio frequency (RF) signals or other wireless signals, orother mediums. The computer readable medium may be, for example but isnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device. More specificexamples of suitable computer readable medium include, but are notlimited to, an electrical connection having one or more wires or atangible storage medium such as a portable computer diskette, a harddisk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), acompact disc read-only memory (CD-ROM), or other optical or magneticstorage device. Computer-readable media includes, but is not to beconfused with, computer-readable storage medium, which is intended tocover all physical, non-transitory, or similar embodiments ofcomputer-readable media.

Various embodiments of the present disclosure may be described hereinwith reference to flowchart illustrations and/or block diagrams ofmethods, apparatus (systems), and computer program products. It isunderstood that each block of the flowchart illustrations and/or blockdiagrams, and/or combinations of blocks in the flowchart illustrationsand/or block diagrams, can be implemented by computer-executable programcode portions. These computer-executable program code portions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce aparticular machine, such that the code portions, which execute via theprocessor of the computer or other programmable data processingapparatus, create mechanisms for implementing the functions/actsspecified in the flowchart and/or block diagram block or blocks.Alternatively, computer program implemented steps or acts may becombined with operator or human implemented steps or acts in order tocarry out an embodiment of the invention.

Additionally, although a flowchart may illustrate a method as asequential process, many of the operations in the flowcharts illustratedherein can be performed in parallel or concurrently. In addition, theorder of the method steps illustrated in a flowchart may be rearrangedfor some embodiments. Similarly, a method illustrated in a flow chartcould have additional steps not included therein or fewer steps thanthose shown. A method step may correspond to a method, a function, aprocedure, a subroutine, a subprogram, etc.

As used herein, the terms “substantially” or “generally” refer to thecomplete or nearly complete extent or degree of an action,characteristic, property, state, structure, item, or result. Forexample, an object that is “substantially” or “generally” enclosed wouldmean that the object is either completely enclosed or nearly completelyenclosed. The exact allowable degree of deviation from absolutecompleteness may in some cases depend on the specific context. However,generally speaking, the nearness of completion will be so as to havegenerally the same overall result as if absolute and total completionwere obtained. The use of “substantially” or “generally” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result. For example, an element, combination,embodiment, or composition that is “substantially free of” or “generallyfree of” an ingredient or element may still actually contain such itemas long as there is generally no measurable effect thereof.

As stated above, for a variety of reasons and to solve a number ofissues in conventional data storage systems, there is a need in the artfor improved data progression in a data storage system, andparticularly, for methods and systems for generating snapshots, as atleast a part of overall data progression, in an on-demand manner, whichcan be particularly desirable in hybrid storage systems utilizing SLCand MLC devices or other hybrid or tiered-based storage. The presentdisclosure improves on conventional systems and processes for dataprogression in a data storage system or other information handlingsystem, such as but not limited to the type of data storage systemsdescribed in U.S. Pat. No. 7,613,945, U.S. Pat. No. 8,468,292, and U.S.patent application Ser. No. 13/429,511. The disclosed improvements canprovide more efficient storage space utilization, and particularly insystems utilizing SLC and MLC devices, can more efficiently utilize thedifferent SSD types to a system's advantage.

In one embodiment of the present disclosure, in a data storage systemhaving SLC and MLC solid state devices, in order to increase system costefficiencies and performance, the data storage system may comprise alower amount of SLC storage space or lesser number of SLC devices ascompared to MLC storage space or MLC devices. Additionally, the datastorage system can be set up, according to the various embodiments ofthe present disclosure, to more regularly or continuously make the SLCstorage space available for new page writes. In one particularembodiment, the MLC devices may be configured to store relatively moreread-intensive data or data pages, being data that is rewrittenrelatively seldomly or is read-only, storing for example but not limitedto, historical snapshot data. Because the read performance of MLCdevices is the same as for SLC devices, but conventionally, MLC devicesare obtainable at lower cost compared to SLC devices of similar storagecapacity, the cost efficiency of the data storage system may beincreased without a decrease in performance.

Accordingly, in one embodiment of the present disclosure, a snapshot orPITC may be moved to MLC storage space as soon as, or generallyimmediately after, the snapshot is taken, and the read performance wouldnot be compromised. The SLC storage space may thus be maintained orreserved for active data or for receiving and handling write requests.This configuration can suitably utilize each of the solid state devicetypes (i.e., SLC and MLC) uniquely to their advantage to help achieve ormaintain high or maximum performances for read and write requests. Inone embodiment, the SLC devices may be configured as RAID 10 storagespace and the MLC devices may be configured as RAID 5 storage space.However, it is recognized that any RAID configuration or combination ofRAID configurations may be utilized on either the SLC and/or MLCdevices.

In a further embodiment, the SLC storage space may be made moreregularly or continuously available by utilizing data progressiontechniques, which may be performed in regular, irregular, or periodicintervals, upon receiving a user request, randomly, and/or continuouslyor substantially continuously. Data progression may be configured tomove or transfer snapshot or PITC data from SLC storage space to MLCstorage space, thereby more making more efficient use of the differenttypes of solid state devices. Additionally, because SLC storage space isutilized primarily for active data or handling write I/O, and MLCstorage space is used primarily for snapshot data, the MLC storage spacemay receive or handle a significantly less amount of write I/O, thusdecreasing the wear out rate of the MLC devices.

In conventional systems, there are certain cases where such dataprogression may not, however, move data quickly enough from one storagetier to another, and in the above embodiments, this may result in theSLC storage space being quickly consumed where the data is notefficiently moved to the MLC storage space. Particularly, inconventional data progression methods, the data may not be moved quicklyenough from one storage tier to another in the following non-limitingexample cases:

-   -   1. where volume data or other data is configured for snapshot        capability but snapshots have not been enabled;    -   2. where volume data or other data is not associated with a        snapshot schedule;    -   3. where volume data or other data is configured under a        snapshot schedule where snapshots are generated relatively        infrequently; and    -   4. where volume data or other data consumes a significant        portion or all of the SLC storage space, which causes the system        to force the SLC storage space into a conservation mode before a        snapshot can be generated based on the configured snapshot        schedule.

In one embodiment of the present disclosure, to better handle the cases,such as those identified above, where the data may not be moved quicklyenough from one storage tier to another, the data storage system may, attimes, force, in an on-demand manner, one or more volumes having themost number of SLC pages relative the other volumes, to take a snapshotof the volume data, which generally renders the data read-only making itsuitable for MLC device storage, and transfer the snapshot data to MLCstorage space or other relatively lower or lower cost storage tier, suchas one or more disk drive tiers. In one embodiment, the system may forcethe on-demand snapshot when the amount of free or available space in theSLC device(s) approaches or reaches a predetermined free spacethreshold. The free space threshold may be set at any suitable amount ofremaining free or available space, such as but not limited to, whenthere is 15% or less available SLC storage space, when there is 10% orless available SLC storage space, or when there is 5% or less availableSLC storage space. Of course, any other amount of remaining SLC storagespace may be used as a threshold, and those given are but a fewnon-limiting examples. This type of snapshot taken in an on-demandmanner is referred to herein as an on-demand snapshot or on-demand PITC.The on-demand snapshot may be identified within the data storage systemusing an attribute value. Once an on-demand snapshot has been taken, andtransferred to a lower tier such as MLC storage space, the data storagesystem may allocate new pages for write I/O of the active PITC, if notalready allocated as part of copy-on-write (COW) algorithm.

In one embodiment, such on-demand snapshots are utilized by the datastorage system only and are not exposed to user. That is, an on-demandsnapshot may be a solely internal snapshot generated for at least thepurpose of converting data to read-only or substantially read onlystatus and move the data to MLC storage space or other relatively lowercost tier storage space. The on-demand snapshot is not typically, and insome embodiments not permitted to be, generated by the user.

In this regard, the on-demand snapshot need not be required to preservepages that are “overwritten” (e.g., in a child PITC via a COWoperation), for example but not limited to, for backup purposes or forview volume creation, described in further detail in U.S. Pat. No.7,613,945, which was previously incorporated herein by reference.Accordingly, where a page or page range is overwritten to a child PITC,for example after a COW operation, the corresponding pages in theon-demand snapshot become unnecessary and generally useless and merelyoccupy space that could otherwise rejoin the free pagepool. If notreturned, therefore, this could lead to increased and unnecessary spaceconsumption, depending on, for example, the number of new page writeI/Os to the volume after an on-demand snapshot is generated. Theincreased and unnecessary space consumption, even in the lower tiers,could starve volumes of user I/O space.

Accordingly, in one embodiment, the pages of an on-demand snapshot thathave been overwritten, rendering them unnecessary, may be reclaimedthrough a novel and advantageous method referred to herein as pruning ofon-demand snapshot pages, or on-demand snapshot prune, or the like.On-demand snapshot prune may operate to return pages to the freepagepool from the on-demand snapshot if a child PITC contains one ormore pages overwriting the corresponding pages of the on-demandsnapshot. On-demand snapshot prune may be configured to operate on onlyon-demand snapshots. On-demand snapshot prune may run at regular,irregular, or periodic intervals, upon receiving a system request,randomly, and/or continuously or substantially continuously.

In one embodiment, on-demand snapshot prune may operate on a particularpage as soon as, or relatively immediately after, a page is allocated ina child of the on-demand snapshot for the same logical block address(LBA) range. Where on-demand snapshot prune is performed on such a pagebasis, the system may load snapshot metadata (if required or desired),update the page address, return the page to the free pagepool, andcommit and unload any updated snapshot metadata. While the page basismethod for on-demand snapshot prune is viable and is one embodiment ofthe present disclosure, such page basis, however, may not be greatlyefficient due to frequent loading and unloading of snapshot metadata,resulting in a lot of read I/Os and CPU cycles, and because committingsnapshot metadata for every page can lead to a lot of metadata updates(i.e., write I/Os). Additionally, the free pagepool metadata will alsohave to be correspondingly updated frequently, resulting in additionalwrite I/Os. Such frequent metadata I/Os may degrade the SSDs morequickly. The above mentioned disadvantages can be reduced or avoidedthrough batch processing of the pages.

One batch processing method 300 for on-demand snapshot prune isillustrated in FIG. 3. On-demand snapshot prune may start at 302 and asan initial step 304 load any metadata (if required or desired) for theon-demand snapshot. In decision step 306, the method may determinewhether all pages of the on-demand snapshot have been checked. If not,the method may proceed to step 308 where a first (if on first pass) or anext (if on a subsequent pass) page of the on-demand snapshot is checkedto see if it has been overwritten in a child PITC. If not, then indecision step 310, the method may return to decision step 306, otherwisein step 312, the page may be returned to the free pagepool, and anycorresponding metadata updated. After returning the overwrittenon-demand snapshot page to the free pagepool, the method may return todecision step 306. If in step 306 it has been determined that all pagesof the on-demand snapshot have been checked, the method may proceed tostep 314 where the metadata may be unloaded and the method may becompleted.

As stated above, on-demand snapshot prune may run at regular, irregular,or periodic intervals, upon receiving a system request, randomly, and/orcontinuously or substantially continuously. In some embodiments, for abatch processing on-demand prune method, the following triggers arenon-limiting examples of triggers that may cause initiation of a batchprocessing on-demand prune operation:

1. Pagepool Conservation and Emergency Mode

-   -   When the free pagepool enters a conservation or emergency mode,        for example, when available disk space has reached a        predetermined minimum free space threshold limit, such as but        not limited to 10%, 5%, or 3%, the data storage system may        trigger performance of on-demand snapshot prune to prune        on-demand snapshot pages, if any are available for pruning as        described above.

2. Periodic Prune

-   -   After an on-demand snapshot is generated for a volume, if the        volume receives a lot of new write requests, then it may fill        the active PITC more quickly and occupy space thus desirably        causing on-demand prune to be run even before conventional data        progression can be performed. In this regard, on-demand prune        can be performed when the active PITC space consumed reaches or        is a multiple of a predetermined threshold non-zero occupied        space limit (such as, but not limited to, 1 GB).

3. PITC Coalesce

-   -   As will be described in further detail below, where a frozen and        expired PITC is converted into an on-demand PITC as part of        coalesce process, then on-demand prune may be initiated on that        on-demand PITC to reclaim space, if applicable.

4. Snapshot Data Progression

-   -   On-demand snapshot prune may be initiated as part of overall        processing of the on-demand snapshot pages. For example,        on-demand snapshot prune may be ran once a day and shall prune        all pages since the last on-demand snapshot prune process. In        still other on-demand snapshot prune methods, prune may be        initiated at any other regular or irregular time intervals or        based upon occurrence or periodic occurrence of any other        suitable event or events.

FIG. 4A schematically illustrates, on the left side, an on-demandsnapshot or PITC 402 and child PITC 404 before on-demand snapshot prunehas been performed, and, on the right side, the same snapshot 406 andchild PITC 408 after on-demand snapshot prune has been performed. On theleft side of FIG. 4A, a total of nine (9) data pages 410 are allocatedbetween the on-demand PITC 402 and the child PITC 404. That is, ninepages of data are currently allocated and unavailable for new writes.However, pages 1, 2, and 5 of the on-demand PITC 402 have been“overwritten” as pages 6, 7, and 9 in the child PITC 404, and as such,pages 1, 2, and 5 of the on-demand PITC become unnecessary and simplyconsume otherwise valuable storage space. After on-demand snapshotprune, as described with respect to FIG. 3 above, has been performed, asillustrated on the right side of FIG. 4A, the on-demand PITC 406 onlystores pages 3 and 4, which have not yet been overwritten in a childPITC, such as PITC 408. However, unnecessary pages 1, 2, and 5 have beenreclaimed and returned to the free pagepool for reallocation. Unliketraditional snapshots and PITCs, as maybe seen from FIG. 4A, in oneembodiment, an on-demand snapshot may not always represent data at timethe snapshot was generated, for example, where an on-demand snapshotprune operation has been completed, and is one reason why, in someembodiments, on-demand snapshots are typically for internal system useonly.

As described above, in many cases, after any given PITC expires, it nolonger needs to be stored in the system nor does it need to be availablefor users. However, there are some cases where the expired PITC can beleft in a frozen state until another snapshot is taken before coalescingis possible, thereby unnecessarily holding allocated pages hostage,resulting in unnecessary space consumption. In this regard, in oneembodiment, such a frozen and expired PITC may be converted into anon-demand snapshot or PITC, as illustrated in FIG. 4B, which on the leftside, schematically shows an active PITC 420 and a parent frozen andexpired PITC 422, and, on the right side, schematically shows the sameactive PITC 424, but the parent frozen and expired PITC has beenconverted to an on-demand snapshot or PITC 426. Once converted to anon-demand snapshot 426, on-demand snapshot prune may be performed on theon-demand snapshot, thereby freeing overwritten pages to the freepagepool upon performance of the prune operation, rather than waitinguntil another child PITC is generated from the active PITC so that thefrozen and expired PITC can coalesce in order to free pages. Theon-demand snapshot 426 may subsequently coalesce when another child PITCis generated; however, at least the overwritten pages may be freedsooner under the on-demand snapshot prune process.

The various embodiments of the present disclosure are advantageous for avariety of reasons. For example, the various embodiment of the presentdisclosure can provide more efficient storage space utilization, andparticularly in systems utilizing SLC and MLC devices, can moreefficiently utilize the different SSD types to a system's advantage.Particularly, in data storage systems utilizing any of the various formsof data progression disclosed or incorporated herein, on-demandsnapshots and the corresponding on-demand snapshot prune may permit thedata storage system to more efficiently utilize SLC devices for handlingthe bulk or all of the write I/Os, and relatively quickly move snapshotor PITC (e.g., read-only) pages to MLC devices when desirable, withoutknowledge to the user, in order to efficiently relieve the SLC storagespace of unnecessary overconsumption and, in the background, handle andreclaim usable space from the on-demand snapshots in MLC storage space.Of course, other advantages of the various embodiments of the presentdisclosure will be, or become, apparent to those skilled in the art.

In the foregoing description, various embodiments of the presentdisclosure have been presented for the purpose of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise form disclosed. Obvious modifications orvariations are possible in light of the above teachings. The variousembodiments were chosen and described to provide the best illustrationof the principals of the disclosure and their practical application, andto enable one of ordinary skill in the art to utilize the variousembodiments with various modifications as are suited to the particularuse contemplated. All such modifications and variations are within thescope of the present disclosure as determined by the appended claimswhen interpreted in accordance with the breadth they are fairly,legally, and equitably entitled.

We claim:
 1. A method of data progression in a data storage systemhaving at least two tiers of storage space, a first tier comprisingstorage space in a single level cell (SLC) solid state device (SSD) anda second tier comprising storage space in a multi-level cell (MLC) SSD,the method comprising: setting a predetermined free space threshold forthe first tier of storage space that is a threshold relating to theamount of free space available on the first tier of storage space;monitoring at least an amount of available free space in the first tierof storage space; when the amount of available free space in the firsttier of storage space decreases to the predetermined free spacethreshold, generating an on-demand snapshot of at least a portion of thedata of the first tier of storage space by designating that data asread-only; transferring the on-demand snapshot to the second tier ofstorage space, thereby freeing the corresponding at least a portion ofdata of the first tier of storage space for new writes; wherein a writeoperation received by the data storage system directed to data stored bythe on-demand snapshot is directed instead to newly allocated storagespace of the first tier of storage space, and the corresponding data inthe on-demand snapshot is considered to be overwritten; and when a pageof the on-demand snapshot contains overwritten data, freeing that pageof the on-demand snapshot, such that the page is no longer associatedwith the on-demand snapshot; wherein the on-demand snapshot is utilizedinternally by the data storage system and is not generally accessible bya user of the data storage system.
 2. The method of data progression ofclaim 1, further comprising, in addition to generating an on-demandsnapshot, generating snapshots of at least a portion of the data of thefirst tier of storage space and transferring at least some of thegenerated snapshots to the second tier of storage space at regularintervals.
 3. The method of data progression of claim 1, wherein thestorage space of the SLC SSD is configured as RAID 10 storage.
 4. Themethod of data progression of claim 3, wherein the storage space of theMLC SSD is configured as RAID 5 storage.
 5. The method of dataprogression of claim 1, wherein the data storage system stores data fora plurality of logical volumes, and wherein the on-demand snapshotcomprises data from a first of the logical volumes utilizing the moststorage space in the first tier.
 6. The method of data progression ofclaim 1, wherein the page of the on-demand snapshot is freedsubstantially as soon as the corresponding data is overwritten.
 7. Themethod of data progression of claim 1, wherein the page of the on-demandsnapshot is freed according to a batch pruning method that operates onat least a portion of the second tier of storage space as a batch andfrees multiple pages of the batch, each page containing data consideredto be overwritten.
 8. The method of data progression of claim 7, whereinthe batch pruning method is triggered when the amount of available freespace in the second tier of storage space decreases to a predeterminedfree space threshold for the second tier of storage space.
 9. The methodof data progression of claim 7, wherein the batch pruning method istriggered according to a periodic schedule.
 10. An information handlingsystem comprising: a data storage subsystem having at least two tiers ofstorage space, a first tier comprising storage space in a single levelcell (SLC) solid state device (SSD) and a second tier comprising storagespace in a multi-level cell (MLC) SSD; a controller managing the datastorage subsystem and configured to: monitor at least an amount ofavailable free space in the first tier of storage space; when the amountof available free space in the first tier of storage space decreases toa predetermined free space threshold, generate an on-demand snapshot ofat least a portion of the data of the first tier of storage space bydesignating that data as read-only; transfer the on-demand snapshot tothe second tier of storage space, thereby freeing the corresponding atleast a portion of data of the first tier of storage space for newwrites; when a write operation is received by the data storage systemdirected to data stored by the on-demand snapshot, direct the writeoperation to newly allocated storage space of the first tier of storagespace, and the corresponding data in the on-demand snapshot isconsidered to be overwritten; and when a page of the on-demand snapshotcontains overwritten data, free that page of the on-demand snapshot,such that the page is no longer associated with the on-demand snapshot;wherein the on-demand snapshot is utilized internally by the controllerand is not generally accessible by a user of the data storage subsystem.11. The information handling system of claim 10, wherein the storagespace of the SLC SSD is configured as RAID 10 storage.
 12. Theinformation handling system of claim 11, wherein the storage space ofthe MLC SSD is configured as RAID 5 storage.
 13. The informationhandling system of claim 10, wherein the controller is configured tofree the page of the on-demand snapshot according to a batch pruningmethod that operates on at least a portion of the second tier of storagespace as a batch and frees multiple pages of the batch, each pagecontaining data considered to be overwritten.
 14. The informationhandling system of claim 13, wherein the controller runs the batchpruning method according to a periodic schedule.